POP3 goes dow every few minutes!

hi,
on my VPS the POP3 service goes down every 3-4 minutes for no reason.
The VPS provider seems not be abl to fix that problem. He set a cronjob to restart automatically POP3 every 10 mins. but this is of course not solution/fix as there are still 6-7 minutes down. Also the VPS is not overloaded and SMTP service for mail.domain.com is disable.

Is there anything we can do to get this fixed or anything we are missing to check?